The present invention relates generally to rotatable members that are able to achieve balanced conditions throughout a range of rotational speeds. The present invention also relates to methods and systems for dynamically balancing rotatable members through the continual determination of out-of-balance forces and motion to thereby take corresponding counter balancing action. The present invention additionally relates to methods and systems for actively placing inertial masses within a rotating body in order to cancel rotational imbalances associated with the rotating body thereon.
When rotatable objects are not in perfect balance, nonsymmetrical mass distribution creates out-of-balance forces because of the centrifugal forces that result from the rotation of the object. This mass imbalance can result in machine vibrations that are synchronous with the rotational speed. Such vibrations can lead to excessive wear and unacceptable levels of noise.
Balancing of a rotatable body is commonly achieved by adjusting a distribution of moveable, inertial masses attached to the body. In general, this state of balance may remain until there is a disturbance to the system. A tire, for instance, can be balanced once by applying weights to it and the tire will remain balanced until it hits a very big bump or the weights are removed. However, certain types of bodies that have been balanced in this manner will generally remain in balance only for a limited range of rotational velocities. One such body is a centrifuge for fluid extraction, which can change the degree of balance as speed is increased and more fluid is extracted.
Many machines are also configured as freestanding spring mass systems in which different components thereof pass through resonance ranges during which the machine may become out of balance. Additionally, such machines may include a rotating body loosely coupled to the end of a flexible shaft rather than fixed to the shaft as in the case of a tire. Thus, moments about a bearing shaft may also be created merely by the weight of the shaft. A flexible shaft rotating at speeds above half of its first critical speed can generally assume significant deformations, which add to the imbalance.
Machines of this kind usually operate above their first critical speed. As a consequence, machines that are initially balanced at relatively low speeds may tend to vibrate excessively as they approach full operating speed. Additionally, if one balances to an acceptable level rather than to a perfect condition (which is difficult to measure), the small remaining xe2x80x9cout-of-balancexe2x80x9d will progressively apply greater force as the speed increases. This increase in force is due to the fact that F is proportional to rxcfx892, (note that F is the out-of-balance force, r is the radius of the rotating body and xcfx89 is its rotational speed).
The mass imbalance distributed along the length of a rotating body gives rise to a rotating force vector at each of the bearings that support the body. In general, the force vectors at respective bearings are not in phase. At each bearing, the rotating force vector may be opposed by a rotating reaction force, which can be transmitted to the bearing supports as noise and vibration. The purpose of active, dynamic balancing is to shift an inertial mass to the appropriate radial eccentricity and angular position for canceling the net imbalance. At the appropriate radial and angular distribution, the inertial mass can generate a rotating centrifugal force vector equal in magnitude and phase to the reaction force referred to above. Although rotatable objects find use in many different applications, one particular application is a rotating drum of a washing machine.
Many different types of balancing schemes are known to those skilled in the art. U.S. Pat. No. 5,561,993, which was issued to Elgersma et al. on Oct. 22, 1996, and is incorporated herein by reference, discloses a self-balancing rotatable apparatus. Elgersma et al. disclosed a method and system for measuring forces and motion via accelerations at various locations in a system. The forces and moments were balanced through the use of a matrix manipulation technique for determining appropriate counterbalance forces located at two axial positions of the rotatable member. The method and system described in Elgersma et al. accounted for possible accelerations of a machine, such as a washing machine, which could not otherwise be accomplished if the motion of the machine were not measured. Such a method and system was operable in association with machines not rigidly attached to immovable objects, such as concrete floors. The algorithm disclosed by Elgersma et al. permitted counterbalance forces to be calculated even when the rotating system (such as a washing machine), was located on a flexible or mobile floor structure combined with carpet and padding between the washing machine and a rigid support structure.
U.S. Pat. No. 5,561,993 thus described a dynamic balance control algorithm for balancing a centrifuge for fluid extraction. To accomplish such balance control, balance control actions may place mass at the periphery of axial control planes on the centrifuge. Related sensor responses to balancing control actions on a centrifuge may be modeled and utilized to determine control actions that would serve to drive an associated system toward a balanced state. Such a system is generally time variant, such that the control models utilized therein may need to be routinely updated based on the measured response to a previous control action, which is a variation of perturbation theory, well known in the art. The control actions may require multiple control actuators; generally one per axial control plane, although multiple actuators at multiple control planes may emulate additional virtual control planes.
A variety of control action actuation techniques have been developed for use with rotating devices or rotating systems, such as washing machines. Such control techniques generally depend on an actuation system based on the placement of mass on a rotating apparatus from its stationary surroundings, requiring accuracy in amount and placement of the counterbalancing mass. A limited amount of mass can be placed at a specific location only once per revolution, and the actuator action is a step action with a flow and transport timing characteristic. On-off actuated valve methods and systems, e.g., solenoid actuated valves, have been developed to place fluid mass on the rotating apparatus so as to achieve balance. These methods and systems suffer from highly variable head pressures from one control action to the next and from inconsistent flow-rate profiles across a single control action, thereby leading to uncertainty in the amount and placement of the counterbalancing mass. Additionally, these method and systems poorly address the need to adjust flow rate such that there is increased flow at lower rotating speeds where balancing generally occurs, and less flow at higher rotating speeds where minor balancing corrections may be required.
Based on the foregoing, it can be appreciated that a method and system are required to place mass on a rotating apparatus from its stationary surroundings, that reduces the dependence on head pressure, improves flow rate consistency within a single control action, and supports differing flow rates to accommodate different control needs across operational speeds. Also, the method and system need to be on the order of complexity, or less, than that of a solenoid actuated valve. The invention disclosed herein addresses these needs and the related concerns.
The following summary of the invention is provided to facilitate an understanding of some of the innovative features unique to the present invention and is not intended to be a full description. A full appreciation of the various aspects of the invention can be gained by taking the entire specification, claims, drawings, and abstract as a whole.
It is one aspect of the present invention to provide methods and systems in which rotatable members can achieve balanced conditions throughout a range of rotational speeds.
It is another aspect of the present invention to provide methods and systems for dynamically balancing rotatable members through the continual determination of out-of-balance forces and motion to thereby take corresponding counter balancing action.
It is yet another aspect of the present invention to provide methods and systems for transferring balancing mass to a rotating system or rotating device in order to dynamically balance the rotating system or rotating device.
In accordance with various aspects of the present invention, methods and systems are disclosed herein for transferring balancing mass to a rotating apparatus from its stationary surroundings, in order to dynamically balance the rotating system. A flow of balancing mass can be continuously provided to the rotating system at a controlled flow rate. The flow of balancing mass can be thereafter discharged at a shutter device integrated with the rotating system, such that the balancing mass passes through a window of the shutter device if the window is open, thereby contributing to the balancing of the rotating system. The balancing mass is generally automatically recirculated if the window of the shutter device is closed.
The shutter device itself may be, for example, a solenoid actuated shutter or a rotating slotted-disk device. The solenoid-actuated shutter may simply be an open-close action with fixed window size. The rotating slotted-disk may have a window that can be configured as an adjustable or fixed window. An adjustable window would be sized for the desired angular span and the slotted-disk would rotate in lock step with the rotating apparatus. A fixed window may accommodate different angular spans via relative speed. This shutter device allows the placement of mass to be very responsive.
The balancing mass may be targeted at the shutter device in order to discharge the flow of the balancing mass through the window of the shutter device. A pump integrated with the rotating system can be utilized to provide the flow of the balancing mass to the rotating system at a controlled flow rate. The flow of balancing mass from the pump generally provides independence from head pressure concerns. The controlled flow rate of the balancing mass may be adjusted through a variable speed pump and can also be adjusted utilizing a nozzle device. The controlled flow rate can be adjusted automatically or otherwise to account for varying rotation speeds of the rotating system at continuous or discrete levels. The varying flow rates are utilized for different control needs such as large mass transfer at lower speeds for initial balance and small mass transfers at higher speeds for fine balance adjustments.